Stratigraphy and Correlation of Middle Cretaceous Rocks Around Uinta Basin, Northeastern Utah and Northwestern Colorado: ABSTRACT

Abstract

On the north side of the Uinta basin, the nonmarine Dakota Sandstone is conformably overlain by the Mowry Shale. The unconformably overlying Turonian Frontier Formation consists of a basal transgressive sandstone and marine shale member that onlaps the Mowry Shale from west to east, and an overlying southeasterly prograding wedge of coastal sandstone and delta-plain deposits. The unconformity between the Frontier and Mowry represents as much as 6 m.y. On the south side of the Uinta basin, the upper Cenomanian-Turonian Tununk Member of the Mancos Shale is separated from the underlying Aptian-Albian Cedar Mountain Formation by a 4-m.y. unconformity. The Cenomanian Dakota Sandstone, not everywhere present, onlaps the unconformity surface from both east and west. The middle turonian Ferron Sandstone Member of the Mancos gradationally overlies the Tununk Member on the west and grades into siltstone of the Tununk eastward. These units are overlain by the deeper water upper Turonian Juana Lopez Member of the Mancos, which has been mapped as the Ferron Sandstone Member on the south side of the basin. Drill-hole log correlations across the east side of the basin indicate that (1) the Albian Mowry Shale on the north side of the basin grades southward into themore » Dakota Sandstone a few miles south of Rangely, Colorado, (2) farther south this Dakota in turn grades into the upper part of the Cedar Mountain formation, and (3) the unconformity between the Mowry and Frontier on the north side is the same as the unconformity between the Cedar Mountain Formations and the Tununk Member (or the Dakota, where present) on the south side.« less